Medication errors constitute a major proportion of the events that lead to significant risks to patients and, for commonly prescribed medications, it is likely that many errors occur in ambulatory settings. Computer-based decision support systems (DSS) offer a solution for improving prescribing patterns and concomitantly improving patient safety, but there are many factors that are still unknown about their use in primary care settings. We propose to develop, implement and evaluate DSS intervention focused on minimizing the barriers to use of these systems to impact patient safety. We will (1) implement decision support systems designed to reduce medical errors; (2) minimize barriers to maximize the probability that the systems will be used; (3) systematically assess the extent to which potential or perceived barriers actually influence DSS use; and, most importantly, (4) assess the impact of DSS on patient safety, targeting preventing the risks of inappropriate medication prescribing. Our target audiences for the decision support intervention are internal medicine residents in an urban academic medical center and primary care physicians throughout the state of Alabama, but primarily in rural areas, who participate in the Alabama Practice Based Research Network (APBRN). We will implement a suite of decision support systems that are designed to reduce medical errors and systematically assess the extent to which potential or perceived barriers actually influence DSS use in ambulatory settings. The methodology also will include a randomized controlled trial to assess the impact on medication error reduction of a DSS intervention implemented on a handheld computer for appropriate risk assessment prior to prescribing certain medications. To assure that all subjects are exposed to comparable cases, unannounced Standardized Patients (SPs) will be used to assess performance and to provide data on interactions during the patient encounter. Finally, in the last year of the project we will have a statewide dissemination conference describing the results of the project. The conference will be targeted on developing an agenda for using DSS to improve patient safety throughout the state of Alabama.